Memory cells and methods of forming memory cells

ABSTRACT

Some embodiments include a memory cell having a first electrode, and an intermediate material over and directly against the first electrode. The intermediate material includes stabilizing species corresponding to one or both of carbon and boron. The memory cell also has a switching material over and directly against the intermediate material, an ion reservoir material over the switching material, and a second electrode over the ion reservoir material. Some embodiments include methods of forming memory cells.

RELATED PATENT DATA

This patent resulted from a continuation of U.S. patent application Ser.No. 14/618,936, which was filed Feb. 10, 2015, and which is herebyincorporated herein by reference; which resulted from a divisional ofU.S. patent application Ser. No. 14/070,407, which was filed Nov. 1,2013, which issued as U.S. Pat. No. 8,981,334, and which is herebyincorporated herein by reference.

TECHNICAL FIELD

Memory cells and methods of forming memory cells.

BACKGROUND

Integrated memory may be used in computer systems for storing data.Integrated memory is usually fabricated in one or more arrays ofindividual memory cells. The memory cells are configured to retain orstore memory in at least two different selectable states. In a binarysystem, the states are considered as either a “0” or a “1”. In othersystems, at least some individual memory cells may be configured tostore more than two levels or states of information.

An example memory cell is a programmable metallization cell (PMC). Suchmay be alternatively referred to as conductive bridging random accessmemory (CBRAM), nanobridge memory, or electrolyte memory. A PMC may useion conductive switching material (for instance, a suitable chalcogenideor any of various suitable oxides) and an ion reservoir materialproximate the switching material. The ion reservoir material andswitching material may be provided between a pair of electrodes. Asuitable voltage applied across the electrodes can cause ions to migratefrom the ion reservoir material into the switching material to therebycreate one or more current-conductive paths through the switchingmaterial. An opposite voltage applied across the electrodes essentiallyreverses the process and thus removes the current-conductive paths. APMC thus comprises a high resistance state (corresponding to the statelacking a conductive bridge extending through a switching material) anda low resistance state (corresponding to the state having the conductivebridge extending through the switching material), with such states beingreversibly interchangeable with one another.

Although there has been effort toward development of PMCs and othermemory cells, there remains a need for improved memory cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example embodiment PMC in cross-sectional side viewreversibly transitioning between a low resistance state (LRS) and a highresistance state (HRS).

FIG. 2 shows an example embodiment memory cell in cross-sectional sideview.

FIGS. 3-7 show a semiconductor construction in cross-sectional sideview, and illustrate process stages of an example embodiment process forforming an example embodiment memory cell.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

A performance aspect of PMCs can be conductivity through the electrodes,with higher conductivity electrodes being desired. Another performanceaspect can be stability of a conductive bridge. Some embodimentsprovided herein utilize an intermediate material between a switchingmaterial and an adjacent electrode to enable characteristics of a memorycell to be tailored to achieve a desired balance between conductivebridge stability and electrode conductivity. The intermediate materialcomprises one or both of carbon and boron. The intermediate material mayimprove reliability of the memory cell as compared to conventionalmemory cells, may improve memory state retention, and may improvedurability of the memory cell as compared to conventional memory cells.Example embodiments are described with reference to FIGS. 1-7.

Referring to FIG. 1, a PMC (i.e., memory cell) 10 is illustrated in twomodes corresponding to a high resistance state (HRS) and a lowresistance state (LRS). The two modes are reversibly interchanged withone another through application of electric fields EF⁺ and EF⁻, with EF⁺being of opposite polarity relative to EF⁻.

The PMC comprises a pair of electrodes 12 and 14, which in someembodiments may be referred to as a first electrode and a secondelectrode respectively. The PMC also comprises a switching material 16and an ion reservoir material 18 between the electrodes. Additionally,the PMC comprises an intermediate material 20 between the firstelectrode 12 and the switching material 16. In the shown embodiment, theintermediate material 20 is directly against an upper surface of theelectrode 12, and directly against a lower surface of the switchingmaterial 16.

Electrodes 12 and 14 may comprise any suitable conductive composition orcombination of compositions; and may be the same composition as oneanother or may be different compositions relative to one another. Insome embodiments, the electrodes may comprise, consist essentially of,or consist of one or more of various metals (for example, tungsten,titanium, ruthenium, tantalum, etc.) or metal-containing compositions(for instance, metal nitride, metal carbide, metal silicide, etc.). Forinstance, in some embodiments the electrode 12 may comprise, consistessentially of, or consist of a titanium-containing composition (forinstance, titanium nitride); and the electrode 14 may comprise, consistessentially of, or consist of tungsten. As other illustrative examples,in some embodiments the electrode 12 may comprise one or more ofruthenium, tungsten and tantalum nitride.

In the shown embodiment, the electrode 12 extends through a dielectricmaterial 13. In some embodiments, such dielectric material may comprise,consist essentially of, or consist of silicon nitride.

The memory cell 10 is shown to have the bottom electrode 12 connected toa conductive line 30, and to have the top electrode 14 connected to aconductive line 32 (diagrammatically illustrated with a box). The lines30 and 32 may be sense and/or access lines coupled to the electrodes,and configured for providing appropriate electric fields across thememory cell during read/write operations. In some embodiments, theillustrated memory cell may be one of a plurality of memory cells of amemory array, and the lines 30 and 32 may be part of a circuitconfiguration utilized to uniquely address each of the memory cells ofthe array. In some embodiments, a “select device” (not shown) may beprovided adjacent the memory cell 10 to reduce undesired current leakageto and/or from the memory cell during utilization of the memory cell ina memory array. Example select devices include diodes, transistors,ovonic threshold switches, etc. The select device may be providedbetween electrode 12 and the line 30 in some embodiments.

Although the electrodes 12 and 14 are shown to comprise homogeneouscompositions, in other embodiments one or both of the electrodes maycomprise multiple discrete compositions; and in some embodiments one orboth of the electrodes may be a laminate of multiple electricallyconductive compositions.

The line 30 may be supported by a semiconductor substrate (not shown).Such substrate may comprise, for example, monocrystalline silicon and/orother suitable semiconductor materials, and may be part of asemiconductor die. Accordingly the memory cell 10 may be part of anintegrated circuit supported by a semiconductor chip.

The switching region 16 may be a solid, gel, or any other suitablephase, and may comprise chalcogenide-type materials (for instance,materials comprising one or more of tellurium, sulfur and selenium),oxides (for instance, aluminum oxide, zirconium oxide, hafnium oxide,tungsten oxide, silicon oxide, etc.) and/or any other suitablematerials.

The ion reservoir material 18 contributes ions which ultimately form oneor more conductive bridges 25 across the switching material 16. The ionreservoir material may comprise any suitable composition or combinationof compositions. In some embodiments, the ion reservoir material maycomprise one or more of aluminum, copper, silver and chalcogen (forinstance, tellurium); and may be configured for contributing aluminumcations, copper cations and/or silver cations for formation of one ormore conductive bridges. The conductive bridges may have any suitableconfiguration and may be filaments of conductive particles (for instanceions or ion clusters) in some embodiments.

In the shown embodiment, the conductive bridge 25 is diagrammaticallyillustrated as being entirely absent in the high resistance state (HRS)configuration of the memory cell. In other embodiments, a portion of theconductive bridge may remain in the HRS configuration of the memorycell.

Although the ion reservoir material is shown comprising a singlecomposition, in other embodiments the ion reservoir material maycomprise two or more different compositions. Similarly, although theswitching material is shown comprising only a single composition, inother embodiments the switching material may comprise two or moredifferent compositions.

The intermediate material 20 may stabilize the memory cell. Forinstance, the intermediate material may stabilize the conductive bridge25 to improve retention and reliability of the memory cell relative toconventional memory cells lacking the intermediate material.Additionally, or alternatively, the intermediate material may functionas a barrier between the switching material 16 and the electrode 12 toalleviate or preclude migration of chemical constituents from electrode12 into switching material 16 and/or vice versa (for instance, thebarrier may preclude undesired oxygen migration from an aluminumoxide-containing switching material to a metal-containing electrode).The intermediate material may comprise stabilizing species correspondingto one or both of carbon and boron. In some embodiments, theintermediate material may comprise, consist essentially of, or consistof one or both of carbon and boron.

In some embodiments, the stabilization provided by intermediate material20 may improve durability of a memory cell (i.e., may extend thelifetime of the memory cell) as compared to conventional memory cellslacking the intermediate material 20. For instance, carbon of theintermediate material may form metal carbide when it interacts withmetal of electrode 12; and such metal carbide may function, at least inpart, as a protective layer proximate the interface of the electrode andthe switching material. Similarly, boron of the intermediate materialmay form a protective metal boride.

The provision of stabilizing species corresponding to carbon and/orboron within the intermediate material 20, rather than dispersing suchspecies throughout electrode 12, may enable conductive properties ofelectrode 12 to be maintained. Such may improve cell performance ascompared to applications in which carbon and/or boron are dispersedthroughout the entirety of the electrode 12.

The conductive bridge 25 is shown to extend to an upper surface ofintermediate material 20, and in the illustrated embodiment does notpenetrate into or through intermediate material 20. In otherembodiments, the conductive bridge may extend at least partially throughthe intermediate material 20.

The intermediate material 20 may be kept thin so that resistiveproperties of the intermediate material impact cell performance onlymarginally, if at all. For instance, in some embodiments theintermediate material may comprise a thickness within a range of fromgreater than 0 Å to less than or equal to about 50 Å; and in someembodiments may comprise a thickness within a range of from greater thanor equal to about 10 Å to less than or equal to about 50 Å.

In some embodiments, utilization of the intermediate material 20 mayenable conductivity of electrode 12 to be enhanced by enablingrelatively exotic materials to be utilized in the electrode 12.Specifically, the barrier properties of intermediate material 20 mayenable materials to be utilized for electrode 12 that could not beutilized in conventional memory cells lacking intermediate material 20.

In some embodiments, the intermediate material 20 may be formed onlyover electrode 12 and not over dielectric material 13. In someembodiments, the intermediate material 20 may be deposited across bothof electrode 12 and dielectric material 13, and may have a samecomposition across the dielectric material as across the electrode. Insome embodiments, at least a portion of the intermediate material may beformed by implanting carbon and/or boron into materials 12 and 13. Insuch embodiments, the intermediate material 20 may comprise a firstcomposition over electrode 12 containing the stabilizing speciesinterspersed with material of electrode 12, and may comprise a secondcomposition over dielectric 13 containing the stabilizing speciesinterspersed with material of dielectric 13. Accordingly, theintermediate material 20 may comprise two different types of regions 31and 33 (as shown), which differ in composition relative to one another.For instance, if electrode 12 comprises titanium nitride, the region 33may comprise boron and/or carbon interspersed with titanium nitride; andif dielectric 13 comprises silicon nitride, the region 31 may compriseboron and/or carbon interspersed with silicon nitride. The compositionwithin region 33 may comprise a total concentration of stabilizingspecies (i.e. boron and/or carbon) within a range of from about 15atomic percent to about 100 atomic percent; in some embodiments within arange of from about 90 atomic percent to about 100 atomic percent; andin some embodiments about 100 atomic percent. The composition withinregion 31 may comprise a similar total concentration of the stabilizingspecies.

In some embodiments, the region 33 may comprise a uniform composition ofthe stabilizing species. In other embodiments, the region 33 maycomprise a gradient of the stabilizing species composition as shown inFIG. 2. Specifically, FIG. 2 shows a memory cell 10 a comprising agradient of stabilizing species concentration (indicated by the arrow40) within an intermediate material 20 a. The illustrated gradientincreases in a direction from the first electrode 12 to the switchingmaterial 16. In some embodiments, an upper surface of the intermediatematerial 20 a directly against the switching material 16 may comprise atotal concentration of stabilizing species (i.e., carbon and/or boron)of from about 90 atomic percent to about 100 atomic percent, and abottom surface of the intermediate material directly against the firstelectrode 12 may comprise a total concentration of the stabilizingspecies of from about 0 atomic percent to less than or equal to about 10atomic percent (and in some embodiments to less than or equal to about 5atomic percent). Similarly, an upper portion of region 31 of theintermediate material may comprise from about 95% to about 100 atomicpercent of stabilizing species, and a lower portion may comprise fromabout zero atomic percent to less or equal to about 10 atomic percent ofthe stabilizing species, with the stabilizing species in the lowerportion being dispersed within a dielectric composition of material 13.

The region 33 of the intermediate material 20 a may comprise stabilizingspecies implanted over and within the composition of electrode 12. Thegradient of FIG. 2 may enable a thin upper region of the intermediatematerial to have the stabilizing properties associated with a highconcentration of boron and/or carbon, and may enable a remainder of theintermediate material to have higher conductivity associated with anincreased concentration of the composition of electrode 12. Thus, thegradient of FIG. 2 may enable an intermediate material to be formedhaving improved conductive properties relative to the homogeneousintermediate material of FIG. 1.

The memory cell 10 a is illustrated in a high resistance state, andaccordingly the conductive bridge 25 (FIG. 1) is not shown.

The memory cells described above may be formed utilizing any suitableprocessing. An example method of forming memory cell 10 is describedwith reference to FIGS. 3-7.

Referring to FIG. 3, a construction 60 is shown at a processing stage inwhich an opening 62 has been formed to extend through dielectricmaterial 13 to an upper surface of the electrically conductive line 30.The opening 62 may be formed with any suitable processing. For instance,a mask (not shown) may be formed over material 13 to define a locationof opening 62, the opening may be transferred through material 13 withone or more suitable etches, and then the mask may be removed to leavethe shown construction of FIG. 3. The mask may comprise any suitablemask; including, for example, a photolithographically-patternedphotoresist mask and/or a mask formed utilizing pitch multiplicationmethodologies.

Referring to FIG. 4, material 64 is formed within opening 62. Thematerial 64 may comprise any of the compositions discussed above withreference to FIG. 1 as being suitable for electrode 12.

Referring to FIG. 5, material 64 is subjected to planarization (forinstance, chemical-mechanical polishing) to form a planarized surface 65extending across materials 13 and 64. Such patterns material 64 into theelectrode 12.

Referring to FIG. 6, intermediate material 20 is formed over materials13 and 64; with such intermediate material comprising one or both ofcarbon and boron. The intermediate material may be formed utilizing anysuitable processing, including, for example, one or more of atomic layerdeposition (ALD), chemical vapor deposition (CVD) and physical vapordeposition (PVD). In some embodiments, at least some of material 20 maybe formed utilizing plasma doping (PLAD). Specifically, construction 60may be provided within a plasma and then suitable ions of thestabilizing species (specifically, carbon and/or boron) are implantedinto the construction to form intermediate material 20. Such implant mayform a homogeneous material, or may form a non-homogeneous material. Insome embodiments, the implant may form a gradient of the type describedabove with reference to FIG. 2. If it is desired to have the uppersurface of material 20 having a higher concentration of the stabilizingspecies than is achieved by the implant, a deposition may be conductedafter the implant to form an upper surface of material 20 comprisingabout 100 atomic percent of the stabilizing species.

In some embodiments, the plasma doping may utilize an energy of fromabout 30 electron volts (eV) to about 10,000 eV; such as, for example,from about 100 eV to about 500 eV. In some embodiments the plasma dopingmay utilize a dose of from about 1×10¹³ ions/cm² to about 1×10¹⁷ions/cm²; such as, for example, a dose of about 1×10¹⁵ ions/cm². In someembodiments, low energy PLAD may provide desired capabilities of tuningand implant characteristics, particularly in a sub-3 KeV regime.

Referring to FIG. 7, the switching material 16 is formed over anddirectly against the intermediate material 20, the ion reservoirmaterial 18 is formed over the switching material 16, and the topelectrode 14 is formed over the ion reservoir material 18. Accordingly,the memory cell 10 is formed.

The memory cells discussed above may be incorporated into electronicsystems. Such electronic systems may be used in, for example, memorymodules, device drivers, power modules, communication modems, processormodules, and application-specific modules, and may include multilayer,multichip modules. The electronic systems may be any of a broad range ofsystems, such as, for example, clocks, televisions, cell phones,personal computers, automobiles, industrial control systems, aircraft,etc.

Unless specified otherwise, the various materials, substances,compositions, etc. described herein may be formed with any suitablemethodologies, either now known or yet to be developed, including, forexample, atomic layer deposition (ALD), chemical vapor deposition (CVD),physical vapor deposition (PVD), etc.

The terms “dielectric” and “electrically insulative” are both utilizedto describe materials having insulative electrical properties. Bothterms are considered synonymous in this disclosure. The utilization ofthe term “dielectric” in some instances, and the term “electricallyinsulative” in other instances, is to provide language variation withinthis disclosure to simplify antecedent basis within the claims thatfollow, and is not utilized to indicate any significant chemical orelectrical differences.

The particular orientation of the various embodiments in the drawings isfor illustrative purposes only, and the embodiments may be rotatedrelative to the shown orientations in some applications. The descriptionprovided herein, and the claims that follow, pertain to any structuresthat have the described relationships between various features,regardless of whether the structures are in the particular orientationof the drawings, or are rotated relative to such orientation.

The cross-sectional views of the accompanying illustrations only showfeatures within the planes of the cross-sections, and do not showmaterials behind the planes of the cross-sections in order to simplifythe drawings.

When a structure is referred to above as being “on” or “against” anotherstructure, it can be directly on the other structure or interveningstructures may also be present. In contrast, when a structure isreferred to as being “directly on” or “directly against” anotherstructure, there are no intervening structures present. When a structureis referred to as being “connected” or “coupled” to another structure,it can be directly connected or coupled to the other structure, orintervening structures may be present. In contrast, when a structure isreferred to as being “directly connected” or “directly coupled” toanother structure, there are no intervening structures present.

In some embodiments, a memory cell comprises a first electrode, and anintermediate material over and directly against the first electrode. Theintermediate material comprises stabilizing species corresponding to oneor both of carbon and boron. The memory cell also comprises a switchingmaterial over and directly against the intermediate material, an ionreservoir material over the switching material, and a second electrodeover the ion reservoir material.

In some embodiments, a memory cell comprises a first electrode, and anintermediate material over and directly against the first electrode. Theintermediate material comprising stabilizing species corresponding toone or both of carbon and boron. The memory cell also comprises aswitching material over and directly against the intermediate material,an ion reservoir material over the switching material, and a secondelectrode over the ion reservoir material. The intermediate materialcomprises a gradient of stabilizing species concentration, with saidconcentration being lowest directly adjacent the first electrode andbeing highest directly adjacent the switching material.

In some embodiments, a method of forming a memory cell comprises formingan intermediate material over and directly against a first electrode,with the intermediate material comprising stabilizing speciescorresponding to one or both of carbon and boron. A switching materialis formed over and directly against the intermediate material. An ionreservoir material is formed over the switching material. A secondelectrode is formed over the ion reservoir material.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

We claim:
 1. A memory cell, comprising: a first electrode comprisingtitanium; an intermediate material over and directly against the firstelectrode, the intermediate material comprising stabilizing speciescorresponding to one or both of carbon and boron; a switching materialover and directly against the intermediate material; an ion reservoirmaterial over the switching material; a second electrode over the ionreservoir material, the second electrode comprising tungsten; andwherein the intermediate material comprises a gradient of stabilizingspecies concentration, with said concentration being lowest directlyadjacent the first electrode and being highest directly adjacent theswitching material.
 2. The memory cell of claim 1 wherein theintermediate material comprises a thickness within a range of fromgreater than 0 angstroms to less than or equal to about 50 angstroms. 3.The memory cell of claim 1 wherein the intermediate material comprises athickness within a range of from greater than or equal to about 10angstroms to less than or equal to about 50 angstroms.
 4. The memorycell of claim 1 wherein a surface of the intermediate material directlyagainst the switching material comprises a total concentration of saidstabilizing species of from about 15 atomic percent to about 100 atomicpercent.
 5. The memory cell of claim 1 wherein a surface of theintermediate material directly against the switching material comprisesa total concentration of said stabilizing species of from about 90atomic percent to about 100 atomic percent.
 6. The memory cell of claim1 wherein a surface of the intermediate material directly against theswitching material comprises a total concentration of said stabilizingspecies of about 100 atomic percent.
 7. The memory cell of claim 1wherein: a surface of the intermediate material directly against theswitching material comprises a total concentration of said stabilizingspecies of from about 90 atomic percent to about 100 atomic percent; anda surface of the intermediate material directly against the firstelectrode comprises a total concentration of said stabilizing species offrom about 0 atomic percent to less than or equal to about 10 atomicpercent.
 8. The memory cell of claim 1 wherein the intermediate materialcomprises carbon.
 9. The memory cell of claim 1 wherein the intermediatematerial comprises boron.
 10. The memory cell of claim 1 wherein theintermediate material comprises carbon and boron.